Conventionally, in a position detector for a vehicle such as a vehicle navigation device for detecting a current position of the vehicle, a combination of a GPS receiver for utilizing a signal from an artificial satellite such as a GPS satellite and an independent sensor such as a vehicle speed sensor for outputting a vehicle speed signal corresponding to a speed of the vehicle and a gyroscope for detecting a rotation angular speed of the vehicle provides to generate an estimation traveling trajectory. Then, the current position of the vehicle is specified on a map with verifying the estimation traveling trajectory and map data. Here, the verification of the estimation traveling trajectory with the map data is defined as a map matching process.
In general, in the position detector for the vehicle, a motion vector of the vehicle is generated from an angular speed of the vehicle detected by the gyroscope and a traveling distance detected by the speed sensor. However, since each of the gyroscope and the speed sensor has an error, it is difficult to estimate the traveling trajectory with high accuracy. Specifically, regarding error factors of each sensor, for example, the gyroscope has an offset error and a gain error, and a distance coefficient error is caused by change of a tire diameter.
To compensate the above errors, the error factor such as the offset error of the orientation change of the vehicle, the gain error of the orientation change, and the distance coefficient error of the speed sensor is defined as one state vector X so that the error factor is modeled with using a Kalman filter in the error estimation process. Then, each error is estimated sequentially based on an output signal of the GPS receiver. Based on the estimated error, the gain correction amount for utilizing the gain correction of the detection value of the gyroscope is modified. This technique is described in JP-A-2009-115545 corresponding to US 2009/0,119,016.
However, in a device described in JP-A-2009-115545, each error is successively estimated under a condition that only a gain error of an attachment angle provides the gain error. The gain error of the attachment angle has a linear relationship with respect to the angular speed. Based on the estimated error, the gain correction amount for utilizing the gain correction of the detection value of the gyroscope is modified. Accordingly, the traveling trajectory of the vehicle is not estimated with high accuracy.